Transonic Systems recently introduced a novel ultrasound indicator dilution method which has the potential to become a routine, economical measurement tool of hemodialysis access flow and recirculation during patient dialysis. We propose to: * Validate these technologies in an animal model, in collaboration with researchers at the NYS College Of Veterinary Medicine at Cornell University; * Support clinical evaluations in key hemodialysis treatment centers in order to establish clinical procedures for the routine measurement and correction of access recirculation, and to develop approaches to improve management of access stenosis based on routine access flow measurement; * Simplify ultrasound indicator dilution technology, apparatus and data analysis so the data collection and interpretation can be done routinely by the dialysis nurse. In Phase I we will perform the animal validation, start our collaboration on clinical evaluations, and simplify the computer software of our research model hemodialysis monitor. In Phase II we will design and construct a new stand-alone hemodialysis monitor for routine clinical use, develop combined arterial + venous bloodline sensing capability, expand collaboration with clinical evaluation centers and prepare for Phase III, commercialization. PROPOSED COMMERCIAL APPLICATION: Access flow and recirculation measurement apparatus to be developed under this grant has the potential of becoming a routine measurement tool for hemodialysis, first as a stand-alone bedside monitor, later as a feature embedded in hemodialysis machines. If successful, this technology will improve hemodialysis patient management, reduce patient management costs and improve patient quality of life. Once the procedure becomes a reimbursable expense, its market consists of: every hemodialysis treatment center.